It has been recognized that the use of multiple different types of fire-indicating sensors can be useful in making determinations as to the presence of a fire condition. Various multi-sensor types of fire detectors are known. These include, for example those disclosed in U.S. Pat. No. 6,967,582 entitled “Detector with Ambient Photon Sensor and Other Sensors”, U.S. Pat. No. 7,068,177 entitled “Multi-sensor Device and Methods for Fire Detection”, U.S. Pat. No. 7,551,096 entitled “Multi-sensor Device and Methods for Fire Detection” and U.S. Pat. No. 7,602,304 entitled “Multi-sensor Device and Methods for Fire Detection”. The noted patents are all assigned to the assignee hereof and incorporated herein by reference.
Existing products using the concepts and ideas from these patents show that optical flame detection is an important part of the multi-sensor fire detection. However, the process of sensing flames in such existing products does not allow for an easy determination of whether the light originates from a flame or it has some other, benign origin. Known detectors often just detect the presence of light in the near infrared portion of the optical spectrum.
There is a need to address several factors that make use of the optical signals difficult. For example, in some instances, temporal patterns of the optical signals, taken every five seconds (or at most every second), represent the only information available to be used to make determination whether a change in the signal is due to flames or not. Additional, normal ambient environments often produce signals in the infrared without flames being present (light bulbs, sunlight, etc.) Consequently, whenever the signal processing does not have sufficient information, it will usually conservatively declare that the observed signal increase is due to flames. This potentially leads to increased frequency of nuisance alarms.
Multi-sensor detectors can limit use of information pertaining to flames to circumstances where the other types of sensors indicate that a fire is developing. There are situations when dangerous flaming fires could be detected more quickly if flame related signals could be regarded as reliable indicators of a fire condition as is the case with other types of fire indicators. For instance a cleanly burning alcohol fire can produce substantial flames but very little smoke and minor temperature rise.
Presently, signals indicating the presence of flame may be dismissed, or given limited weight, because other fire indicators such as smoke and temperature are not significant enough to determine that a fire is developing or present in a region. More reliable flame detection could speed detection of flaming fires.